Dew heater power consumption

[rcheshire (Rowland)]

Hi.

I'm working on a microcontroller setup for a small dew heater and wondering how much current a typical system uses.

The figures I came up with, indicate that 75mm of 22 gauge Nichrome wire requires 500mA for a 20C increase in temperature.
Increase in R with temperature is 0 for practical purposes.

I am interested in knowing what values others measure with their working dew heater. Parameters would be;

Nichrome wire length

Total resistance of the heating circuit.

Voltage across the Nichrome wire.

This will be very helpful to work out realistic performance and set more accurate parameters for the microcontroller PWM output, particularly as the dew heater will reference other temperature readings to set the correct temperature.

Many thanks

Rowland.

[2stroke (Jay)]

Couldn't you just run a temp sensor back for heating source and also an ambient temp sensor to help work out whats needed for dew point?

[Visionoz (Bill)]

Hi Rowland

Perhaps you've already read this? - http://www.dewbuster.com/heaters/nichrome.html

HTH
Cheers
Bill

[rcheshire (Rowland)]

Thanks Jay and Bill.

Space is very restrictive and adding a temp sensor impossible, besides the added complexity. I guess my question is about getting an idea of representative parameters. Probably redundant given Bill's article which I missed previously. I'll work with that for now.

I will use an existing ambient temp sensor to register a preconfigured heating schedule then step the dew heater temperature down using a push button. I need complete control over the system with the ability to set the temperature of the heater accurately. Not sure if its achievable.

[rcheshire (Rowland)]

This is the proposed circuit diagram.

PWM is not available with "Every Circuit" and so I have emulated it with FET gate input voltage at 50% and a corresponding 6v (12v) on the heating side.

Those are the numbers to raise 75mm of Nichrome wire 20C - data from various tables listing the wire properties.

I guess it's time to experiment.

PWM frequency is Arduino native 490hz with a NXP - PSMN1R6-30PL MOSFET to switch the system voltage at the required duty cycle for a given heater temperature. Identical, in principle, to the DSLR Peltier cooling circuit.